The present invention relates generally to detection and analysis of gaseous components and more particularly to a hand-held detection system using gas chromatography and/or ion mobility spectrometer.
Gas chromatography is an established analytical technique for separating the components of a gaseous mixture as the mixture flows through a tubular column. There are many different ways of injecting the initial sample into the column and performing the separation. For example, one way of carrying out the separation in open tubular columns is shown in FIGS. 1a and 1b. In this method, valve 1 admits a small volume of the sample flowing through the loop 2 into the column 3 when the valve is switched from the sampling position shown in FIG. 1a to the injection position shown in FIG. 1b. This volume of sample is then carried down the column by a flow of carrier gas through the port 4 and 5 of the valve and separated into its components when it interacts with the column wall coated with the appropriate separating medium. The net result is that the components exit the column as separate volumes at different times. The time between the injection and the exit of a component is called its retention time. The components are detected by an appropriate detection system, for example, an electron capture detector (ECD) or a thermal conductivity detector. The signal generated by the detector (the chromatogram) can then be plotted out for analysis.
The speed at which analysis takes place in this system is dependent on several factors including the type and length of the column, its temperature and the velocity of the carrier gas in the column. In general total analysis times are in the order of minutes to hours. Sample preparation and injection can take several minutes to hours depending on the nature of the sample. Thus for real time analysis this process needs to be speeded up considerably.
Real time analysis is highly desirable when using the technique of gas chromatography for quickly detecting and identifying compounds contained in narcotics and explosives. Then sampling and detection systems based on gas chromatography can be used for checking suspicious objects which could contain explosive devices or controlled drugs and narcotics. Such devices are useful at border crossings and airports for identifying and preventing drug smuggling or terrorist activity. Therefore, it is also highly desirable to make such detection system portable and operable in real time.
Moreover, it is also desirable to make such systems battery operable. Gas chromatography of drug or explosive samples require that the sampling separation systems work at high temperatures typically in the region of 100 to 300 degrees Celsius. Presently, there are no energy efficient or portable GC-IMS devices which can operate in the high temperature regime for analyzing drugs or explosives because power requirements for gas chromatography systems usually preclude battery operated portable systems of practical size and weight. Therefore, it is also highly desirable to have a gas chromatography system with minimum power consumption without sacrificing performance.
The present invention provides a novel design and method of operation for a pulsed high speed sampling and gas chromatographic (GC) separation system which is capable of sampling and analyzing particles and vapors containing drug and explosive residues in less than twenty seconds and which at the same time consume very little power. The speed and power savings provided by the present invention uses a heat-on-demand (HOD) technology explained below.
There are several important advantages for using the pulsed analysis technique in simple, portable, low power GC-IMS sample gathering and analytical system as disclosed by the present invention. Because of the pulsed nature of the system, power consumption takes place only when the system is analyzing, greatly increasing the overall energy efficiency of the system compared to static systems where the components are always maintained at high operating temperatures. This makes its use practical in hand-held analytical devices using batteries as power sources.
Moreover, the pulsed heating sequence avoids the use of valves to switch a sample packet into the column as is done in static high temperature systems, making the system simpler and more reliable.
Advantageously, the system of the present invention operates as one integrated system for sample gathering, analysis, and data presentation, thus, making it an ideal portable real-time analytical instrument for many applications, including drug and explosive checks and searches at border points, airports, etc., and also for air quality monitoring.
Furthermore, the present invention utilizes an ion mobility spectrometer (IMS) device as a second analyzer. using the IMS greatly increases the overall selectivity and sensitivity of the instrument without adversely affecting its performance or energy efficiency. In the present invention the IMS device is preferably a xe2x80x9ccoldxe2x80x9d IMS device which deliberately operates at a temperature low enough such that the sample vapors introduced into the IMS actually condense in the IMS in a fraction of a second after their introduction. The deliberate trapping of the vapors in the IMS effectively removes the sample from the ionization process because after condensation, the vapor pressure of the compound at the operating temperature of the IMS is so low as to be negligible. Since the compound is no longer present in the vapor form, ion production no longer takes place at a sufficient rate as to be detectable. The process of sample introduction in such a cold IMS is different from sample introduction in conventional IMS devices. The sample is first transported in the vapor form to the entrance of the reaction region at a temperature several tens of degrees higher than the temperature of the reaction region and the temperature of the carrier gas flowing in the reaction region. As the sample vapor enters the reaction region, it encounters the colder gas in the region and starts to cool down. Before the cooling takes place, however, the reactant ions present in the reaction region rapidly convert a portion of the vapor sample into product ions which are subsequently swept away by an electric field into a drift region. The rest of the sample condenses on the walls of the reaction region and is no longer available for ionization reactions in the vapor phase.
The IMS of the instant invention operates at essentially constant temperatures. As a result, the combination of the cold IMS and the xe2x80x9cheat-on-demandxe2x80x9d gas chromatographic (GC) separation system of the present invention greatly eliminates the power requirements needed for keeping the device continuously heated, thus making the system ideal as a battery operable portable detection device.
Furthermore, the combination of the cold IMS and the xe2x80x9cheat-on-demandxe2x80x9d gas chromatographic (GC) separation system of the present invention is encased in a portable closure so that it may be hand-carried and ported easily. Moreover, the case preferably includes a display portion where a display device may be attached to provide information regarding the samples detected.
Further features and advantages of the present invention as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.